Tech Talk - letters from March 2010

March '10

Q&A from Hemmings Classic Car

Idling Out of Control
Q: I live in Australia and own a 1990 Chevrolet Caprice, Canadian built, which occasionally stalls whilst idling in drive at traffic lights. It has a 305-cu.in V-8 with throttle body injection and an automatic transmission. This happens usually at partial warm up of the engine after a mile of driving. Other times it's okay, hot or cold.
Also, this phenomenon occurs with the headlamps on while driving into my garage in the dark, low speed and idling. Parts replaced have been the throttle position indicator, air bleed valve and earlier, the electric fuel pump. The engine will always re-start immediately. Any clues?
Sid Edwards
Via e-mail
According to Ray Bohacz, he of Mechanical Marvels fame in this magazine, "Ask Ray" our Q & A column in Hemmings Muscle Machines, and author of a book on fuel injection tuning, it's common for the throttle plate in these cars to close too far, sealing off the air intake and causing the intermittent stalling you're experiencing at low RPM and under a load. This is particularly true if the idle air control (IAC) has been replaced.Resetting it requires a little finagling, but here's the procedure Ray recommends:Turn the key to the "on" position (don't start the car) and locate the assembly line data link or ALDL connector under the dash. With a jumper wire or paper clip refashioned into the shape of a U, jump the A terminal to the B terminal. This activates the "field service mode" and will extend the plunger on the idle air control to the full-lock position.With the jumper in place and the key on, disconnect the plug on the IAC, then remove the jumper and start the engine. There is an idle screw on the TBI, but it's plugged off to prevent tampering. Since we'll be tampering, we need to extract the plug and then adjust the Torx head screw behind it. Have an assistant put the transmission in drive and hold his foot on the brakes while you adjust the screw to 550-600 RPM. Then reconnect the plug to the IAC.Storage Issues
Q: I keep my 45-year-old Oldsmobile in a heated garage. I drive it two to three times per month (approximately 40 miles per month) throughout the year. I haven't been filling it up, but I maintain the tank between ¼ to ½ full, adding gasoline as needed (two to four gallons per month) and some Marvel Mystery Oil. Since it's in a heated garage and I add fresh gasoline periodically, is it necessary to keep the gas tank full to avoid condensation?
Bill Chimento
Whitestone, New York
Strictly from what you're describing, I'd say no. If your Olds enjoys climate control and you're driving it around a little every couple of weeks, you should be fine. I realize the weather in your part of the state is a little more temperate than in my neck of the woods, but if you do find yourself snowed in, it wouldn't hurt to add some STA-BIL to ensure that the gas stays fresh.Tap or Distilled
Q: I have a 1936 Lincoln "K" LeBaron Roadster. The engine has aluminum cylinder heads, a cast-iron block and copper head gaskets. What would be the best coolant solution using today's technology to prevent corrosion of the aluminum heads? If water is to be used with an additive, should it be distilled, purified or tap water?
Ray Schreffler,
Roseville, California
Don't use tap water; distilled water is definitely the way to go if you want to keep the system clean. If the car is never going to be exposed to freezing temperatures, straight water with a corrosion additive from your corner auto parts store will work. If freezing is a concern, use a 50/50 mix of anti-freeze/coolant or buy the pre-diluted 50/50 stuff to save having to buy distilled water. I understand your concern about the aluminum heads corroding; using distilled water and a corrosion additive and or anti-freeze/coolant and changing it in accordance with the manufacturer's recommendations should be enough. If you'd like to take another step, aluminum radiator manufacturers sell a sacrificial anode, like the one in your home's water heater, that can be inserted in place of the radiator's drain plug. The problem will be finding one that will work in your vintage Lincoln's radiator. Similarly, there are radiator caps with anodes attached that would also help draw the corrosion away from your cylinder heads. However, most on the market these days are high-pressure caps. Perhaps it would be possible to buy one of those and then devise a way to attach the anode to your existing cap?Reader Feedback
I rightfully received a couple dozen emails addressing a question in HCC #64 reminding me that torque specs are given on dry fasteners, not fasteners coated with anti-seize compound or oil. Most of them went something like this particularly well-written response ...
I picked up your magazine on a recent flight home and needed to comment regarding your answer on the snapped bolts. You gave some valid suggestions, but were off on one of the main problems. When a bolt is tightened to a given specification, it is usually given to an unlubricated connection. Bolts are essentially an inclined plane and work due to friction. If the threads are lubricated, then you need to reduce the torque specification by 15-25 percent of the original value. Bolt plating can also affect the torque spec as the plating acts like a dry lubricant. Always follow the manufacturer's specifications, but know that what you might have changed from the original settings, like "bolt strength," "material," and "lubrication," can adversely affect the value.One other point to look at would be the accuracy of the torque wrench. Most wrenches have a +/- tolerance and can get out of calibration from misuse and neglect, so I would do like you mentioned: Use caution, start low and work your way up to the torque spec and never overtighten the bolt.
Kevin Sharpe
Poestenkill, New York

This article originally appeared in the March, 2010 issue of Hemmings Classic Car.